The present invention relates to the design and construction of mobile telephone systems. In particular it relates to a test transmitter for verifying the positioning of antennas in such a system and a method for manufacturing such a test transmitter.
Mobile telephony systems for indoor use are being used to an increasing extent. A common and practical solution for the implementation of indoor mobile telephony systems is to use a distributed antenna system with several antennas, each transmitting with a low output power, connected to one Radio Base Station (RBS). Ideally, the antennas should be distributed in the building in such a way as to enable a 100% coverage. At the same time, the number of antennas should be kept as low as possible for economic and other reasons.
One of the main problems when designing the distributed antenna system is to decide where the antennas should be positioned. To aid in this, the designers may rely completely on experience, or a prediction tool may be used. A prediction tool is a computer based tool that simulates the actual environment in which the antennas are to be placed, based on mathematical models. A digital xe2x80x9cmapxe2x80x9d of the area is shown, and parameters such as wall attenuation and the signal power of the antennas may be set. Antennas are placed in the simulated environment and the signal power is measured in a number of points in the space. While measuring, the parameters may be changed, antennas may be moved in the simulated environment, etc.
Neither experience nor prediction tools will give a perfect result. Parameters such as wall attenuation and radio wave interference have to be estimated or predicted, and the estimates will deviate more or less from the real values. As the number of users of indoor mobile telephony systems increases, so does the need for proper planning of the indoor cells.
Therefore, the antenna positions should be verified before the installation of the whole system. There is a need for a verification system enabling quick and easy verification of the distribution of antennas at a low cost, while still producing a reliable result.
It is possible to verify the cell plan before the installation of the antennas, by use of a Continuous Wave (CW) test transmitter and a test receiver, using analogue Radio Frequency (RF) signals. The test transmitter is positioned where the base station or antenna is to be placed, and the signal from the test transmitter is registered in different positions using a test receiver.
Today a number of test radio network cells exist for outdoor use, for example the PCS-20 and the Cell-20 from Moffet, Larson and Johnson, Inc. (MLJ) or the TS9953 from Rohde and Schwarz. These test cells are all fairly large and heavy, typically 10-30 kg, and cumbersome to move around, and thus are not suitable for indoor use.
They are also quite expensive, and require considerable manual operation, which limits the number of test transmitters that can be used.
One test transmitter from MLJ, intended for indoor use, has a transmit power of up to 1 W and weighs 0.7 kg.
All of the above mentioned test transmitters transmit only a continuous wave, with no information modulated onto it. Thus, the signal from such a test transmitter cannot be distinguished from any other signals, which causes problems in areas where signals from other signal sources also occur. When testing an indoor antenna configuration, it is desirable to be able to test the whole configuration in one operation. This requires that the signals from the different test transmitters can be distinguished from each other, which is not possible if each transmitter only transmits a continuous wave.
A continuous wave transmitter from Rohde and Schwarz, TS9953, may be combined with GSM test equipment TS9951 or TS9958. This test equipment simulates GSM downlink signals, which are modulated onto the continuous wave and transmitted. In this way, each transmitter can be made to transmit a unique signal. Thus, two units are needed. The continuous wave transmitter is rack mounted, and it is impossible for one person to transport it. The output power may be set to 20, 50 or 100 W, and it is clearly not suitable for indoor use.
Normally, when testing the antenna or base station configuration, only one test transmitter is used. This test transmitter is placed at the location planned for an antenna. The test transmitter, which is quite heavy, must be transported to the appropriate location and the antenna must be installed. The signal power in different positions around the antenna is measured. The test transmitter is then moved to a new location, the antenna is installed and measurements are made again. It is not feasible for practical and economical reasons, to use more than one test transmitter at a time. Thus, in practice, the antenna configuration is never tested as a whole.
Also, the power supply is a problem: either an adapter must be used to connect to the mains, or a battery must be used, which is in itself heavy and has limited capacity.
It is an object of the invention to provide a cell test device for cellular telecommunications systems that is easy to use.
It is another object of the invention to provide a cell test device for cellular telecommunications systems that is suitable for indoor use.
It is another object of the invention to provide a cell test device that allows the testing of the whole antenna configuration in one operation.
It is yet another object of the invention to provide a cell test device for cellular telecommunications systems that is easily portable.
It is still another object of the invention to provide a cell test device for cellular telecommunications systems that allows a very precise positioning of antennas for optimizing the antenna distribution.
It is another object of the invention to provide a cell test device for cellular telecommunications systems that is flexible and inexpensive compared to prior art cell test devices.
These and other objects are achieved by the present invention by a test transmitter for a mobile telecommunications system comprising base stations transmitting in a downlink frequency band and portable units for receiving and transmitting, transmitting in an uplink frequency band, said portable units each comprising a portable unit casing, a portable unit transmitter part and a portable unit receiver part, said transmitter part comprising a portable unit microphone, a portable unit channel coding unit, a portable unit interleaving unit, a portable unit modulator unit, a portable unit transmitter unit adapted to the uplink frequency band, and a portable unit antenna, said test transmitter comprising a unit for generating a data stream, a said portable unit modulator unit and a transmitter unit adapted to the downlink frequency band.
In a preferred embodiment, the test transmitter also comprises a said portable unit channel coding unit and a said portable unit interleaving unit. It may be comprised in a said portable unit casing, and may be connectable to all standard peripheral equipment used with said portable units, such as batteries, amplifiers and antennas.
In a preferred embodiment the mobile test transmitter is based on a standard mobile telephone, which is modified to perform the functions required by a test transmitter.
The teachings of the invention are applicable to any type of mobile telephone, including Time Division Multiplex Access (TDMA), Code Division Multiplex Access (CDMA) and Frequency Division Multiplex Access (FDMA).
The invention offers the following advantages:
The mobile test transmitter is small, light, easily portable and can be used with standard mobile telephone accessories, that is, it is easy to use in field measurements.
It is possible to alter the content of the transmitted signal, thus giving a signal that may be identified even in an area with many different signal sources.
The signal produced by the mobile test transmitter is the same signal as transmitted by a base station and will therefore be perceived as a base station by a mobile telephone, thus enabling measurements with standard radio network measurement tools.
The low cost and small size of the mobile test transmitter according to the invention, and the possibility to vary the transmitted signal enables the use of several mobile test transmitters at the same time, and thus enables the testing of the whole combination of antennas in one operation. This also makes it easy to change the position of one or more antennas while testing.
Standard peripheral equipment for mobile telephones, such as batteries and antennas, may be used together with the mobile test transmitter.
The receiver functions in a mobile telephone may be used to make the test transmitter a combined transmitter/receiver.
A device that can mimic a control channel broadcast signal from a base station, may be used to create events in an existing mobile telephone environment for test purposes. The mobile test transmitter will serve as a portable radio network cell for test purposes.
A Man-Machine Interface (MMI) is provided in an easy manner by use of the standard display and keypad of the mobile telephone, or by connecting the mobile test transmitter to a Personal Computer (PC) comprising control software.